sq-23377 and Pancreatic-Neoplasms

Using the whole-cell patch-clamp technique, a calcium-activated chloride conductance (CACC) could be elicited in HPAF cells by addition of 1 microM ionomycin to the bath solution (66 +/- 22 pA/pF;Vm + 60 mV) or by addition of 1 microM calcium to the pipette solution (136 +/- 17 pA/pF; Vm + 60 mV). Both conductances had similar biophysical characteristics, including time-dependent inactivation at hyperpolarising potentials and a linear/slightly outwardly rectifying current/voltage (I/V) curve with a reversal potential (Erev) close to the calculated chloride equilibrium potential. The anion permeability sequence obtained from shifts in Erev was I > Br >/= Cl. 4,4'-Diisothiocyanatostilbene disulphonic acid (DIDS, 500 microM) caused a 13% inhibition of the current (Vm + 60 mV) while 100 microM glibenclamide, 30 nM TS-TM-calix[4]arene and 10 microM tamoxifen, all chloride channel blockers, had no marked effects (8%, -6% and -2% inhibition respectively). Niflumic acid (100 microM) caused a voltage-dependent inhibition of the current of 48% and 17% (Vm +/- 60 mV, respectively). In freshly isolated human pancreatic duct cells (PDCs) a CACC was elicited with 1 microM calcium in the pipette solution (260 +/- 62 pA/pF; Vm + 60 mV). The presence of this CACC in human PDCs could provide a possible therapeutic pathway for treatment of pancreatic insufficiency of the human pancreas in cystic fibrosis.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Action Potentials; Adenocarcinoma; Anions; Calcium; Chelating Agents; Chloride Channels; Egtazic Acid; Electric Conductivity; Humans; Iodides; Ionomycin; Male; Pancreatic Ducts; Pancreatic Neoplasms; Tumor Cells, Cultured

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) may play a key role in the regulation of insulin secretion. We obtained evidence for the presence of CaM kinase II and its substrate, a 84-kilodalton (kDa) protein, in mouse insulinoma MIN6 cells. CaM kinase II from MIN6 cells has one subunit of 55 kDa, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is autophosphorylated in a Ca2+/CaM-dependent manner, and phosphorylates several substrates that serve for rat brain CaM kinase II. In the membrane fraction of MIN6 cells, we identified a 84-kDa protein that was immunoreactive with the antirat brain synapsin I antibody. One-dimensional phosphopeptide mapping by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed the sites of the phosphorylation by cAMP-dependent protein kinase (cAMP kinase) and that by CaM kinase II to be site 1 (10 kDa) and site 2 (30 kDa), respectively, therefore, the same as for rat brain synapsin I. In this context, we tentatively termed it synapsin I-like protein. In 32P-labeled cells, nonfuel insulin secretagogues, such as ionomycin, KCl, and tolbutamide, and a fuel secretagogue, glucose, stimulated autophosphorylation of CaM kinase II and the phosphorylation of synapsin I-like protein. These secretagogues potentiated the Ca(2+)-independent activity of CaM kinase II and secretion of insulin from MIN6 cells. The 84-kDa protein is apparently a newly identified member of the synapsin family. We suggest that CaM kinase II regulates insulin secretion via phosphorylation of synapsin I-like protein.

Topics: Animals; Autoradiography; Calcium; Calcium-Calmodulin-Dependent Protein Kinases; Electrophoresis, Polyacrylamide Gel; Insulin; Insulin Secretion; Insulinoma; Ionomycin; Mice; Mice, Transgenic; Pancreatic Neoplasms; Phosphorylation; Potassium Chloride; Substrate Specificity; Synapsins; Time Factors; Tolbutamide; Tumor Cells, Cultured

Brief phorbol ester treatment of BON cells results in a persistent release and cellular depletion of immunoreactive chromogranin A (CGA-IR) and neurotensin (NT-IR) cell contents. The purpose of the present study was to characterize the effects of 12-O-tetradecanoyl phorbol-13-acetate (TPA) on the secretion, biosynthesis, and steady-state messenger RNA (mRNA) levels of chromogranin A (CGA) and of a coresident peptide, neurotensin, by a novel human pancreatic carcinoid cell line, called BON. Acute TPA treatment (100 nM, 1 h) of BON cells resulted in 20- and 40-fold elevations in release of CGA-IR and NT-IR, respectively; and a 70-90% depletion of CGA-IR and NT-IR cell contents. TPA treatment also increased the biosynthetic rate of CGA-IR. Steady-state mRNA levels of CGA and NT/N (neurotensin/neuromedin N) were unchanged. Cell contents of CGA-IR and NT-IR were not replenished for a period of up to 6 days; secretion of CGA-IR and NT-IR persisted. In addition, BON cells failed to release CGA in response to stimulation by ionomycin and A23187 several days after acute TPA treatment. Our data indicate that the lack of replenishment of cell contents of CGA-IR and NT-IR is not due to decreases in steady-state CGA-IR and NT-IR mRNA levels, nor is it due to a decrease in biosynthesis of CGA-IR, but it is the result of a loss in the ability of TPA-treated BON cells to store and secrete CGA-IR and NT-IR in a regulated manner. These effects of TPA are mediated through the PKC pathway.

Topics: Analysis of Variance; Blotting, Northern; Calcimycin; Carcinoid Tumor; Cell Division; Cell Line; Chromogranin A; Chromogranins; Dose-Response Relationship, Drug; Gene Expression; Humans; Ionomycin; Kinetics; Methionine; Neurotensin; Pancreatic Hormones; Pancreatic Neoplasms; Peptide Fragments; RNA, Messenger; Sulfur Radioisotopes; Tetradecanoylphorbol Acetate; Time Factors; Tumor Cells, Cultured

The importance of Ca2+ in the regulation of secretion is well-known. However, recent experiments suggest that a rise in intracellular Ca2+ (Ca2+i) does not necessarily trigger secretion in pancreatic acinar cells. In AR4-2J cells the role of the Ca2+ mobilization induced by cholecystokinin/gastrin (CCK/G), which is dependent of the intracellular calcium store and the calcium influx operating through voltage-dependent calcium channels, has never been directly demonstrated. Therefore, we attempted to determine whether Ca2+i and/or extracellular Ca2+ (Ca2+e) mobilized by CCK/G plays a role in the amylase secretion of these cells. We measured the [Ca2+]i by spectrofluorometry and amylase release in different experimental procedures modulating the two pools of calcium. Ionomycin increased both [Ca2+]i and amylase related. In Ca(2+)-depleted cells or in the presence of thapsigargin the transient rise in Ca2+i and the amylase secretion induced by CCK/G were suppressed. A 50 mM K+ solution or Bay K 8644, which activated the Ca2+ influx, did not induce any variation of the basal amylase secretion. Moreover, amylase secretion induced by CCK/G did not change significantly in Ca(2+)-free medium or in the presence of nifedipine. These results indicate that in AR4-2J cells, amylase secretion is dependent of the large increase in Ca2+i induced by CCK/G and independent of the Ca2+ influx through voltage-dependent calcium channels dihydropyridine sensitive.

Topics: Amylases; Animals; Calcium; Calcium Channel Blockers; Calcium Channels; Cholecystokinin; Enzyme Inhibitors; Gastrins; Intracellular Fluid; Ion Channel Gating; Ionomycin; Ionophores; Nifedipine; Pancreatic Neoplasms; Rats; Spectrometry, Fluorescence; Terpenes; Thapsigargin; Tumor Cells, Cultured

We have studied the effects of acetylcholine (ACh), and other agents that modulate pancreatic bicarbonate secretion, on the anion permeability of a human ductal adenocarcinoma cell line (BxPC-3). Anion permeability was monitored using an 125I efflux assay. ACh (10 microM) markedly stimulated 125I efflux from BxPC-3 cells and this response was abolished by atropine (10 microM), indicating that it is mediated by muscarinic receptors. Using transport inhibitors and ionophores, we obtained data indicating that some of the ACh-induced 125I efflux results from the opening of K+ channels, which would hyperpolarise the cell and increase the electrical driving force for 125I exit. The remaining ACh-induced 125I efflux is not mediated by anion exchangers or by Na+/K+/2Cl- cotransporters, and is probably explained by activation of an anion channel in the BxPC-3 cell membrane. Ionomycin (0.5 microM) caused a small rise in 125I efflux, indicating that this process can be triggered by an increase in intracellular calcium concentration. ATP (100 microM), ADP (100 microM), bombesin (10 nM), and cholecystokinin (CCK) (10 nM) also stimulated 125I efflux, indicating that receptors for these agents are expressed on BxPC-3 cells. We speculate that bicarbonate secretion from the human pancreas could be modulated by ACh, ATP, bombesin, and CCK via a direct effect on the duct cell.

Topics: Acetylcholine; Adenine Nucleotides; Adenocarcinoma; Adenosine Triphosphate; Bombesin; Cholecystokinin; Humans; Iodine Radioisotopes; Ion Channels; Ionomycin; Pancreatic Neoplasms; Potassium Channels; Tumor Cells, Cultured

The objective of these experiments was to investigate the influence of activation of three second messenger systems (protein kinase-C, adenylate cyclase-cAMP, and calcium mobilization) on the secretion of pancreastatin (PST) and chromogranin-A (CGA) by a human pancreatic carcinoid cell line (BON) in tissue culture. Stimulation of protein kinase-C by a phorbol ester (0.025-7.5 microM) caused a significant dose-related release of PST (186 +/- 22-4271 +/- 228% over controls). Treatment of BON cells with graded doses of 8-bromo-cAMP (0.14-3.0 mM) and isobutylmethylxanthine (IBMX; 0.01-1.0 mM) also stimulated a dose-related release of PST (107 +/- 22-284 +/- 28 and 16 +/- 12-1076 +/- 100% over controls, respectively). Incubation of BON cells with ionomycin (0.134-13.4 microM) increased the release of PST (102 +/- 15-554 +/- 21% over controls) in a dose-related manner. A combination of IBMX and ionomycin resulted in an additive effect, whereas treatment with a phorbol ester plus IBMX resulted in a synergistic effect on PST release. Pretreatment of BON cells with monensin, an agent that prevents processing of precursors to smaller peptides, significantly decreased PST, but not CGA, secretion in response to phorbol ester or ionomycin. These findings indicate that protein kinase-C, cAMP, and Ca2+ mobilization participate in CGA and PST secretion. Although the observation that secretions of PST and CGA in response to theophylline are quantitatively associated, the absence of a quantitative relationship in the release patterns of PST and CGA in response to phorbol ester and ionomycin do not support a simple precursor-product relationship between CGA and PST. The monensin experiments are consistent with the notion that PST is derived from CGA in BON cells.

Topics: 1-Methyl-3-isobutylxanthine; 8-Bromo Cyclic Adenosine Monophosphate; Carcinoid Tumor; Cell Line; Chromatography, Gel; Chromogranin A; Chromogranins; Humans; Ionomycin; Kinetics; Monensin; Pancreatic Hormones; Pancreatic Neoplasms; Phorbol Esters; Radioimmunoassay; Second Messenger Systems; Theophylline

In studying the regulation of insulin secretion by phorbol esters, we examined their effects on the cytosolic free Ca2+ concentration ([Ca2+]i), using the Ca2+ indicator fura-2 in the rat insulin-secreting beta-cell line RINm5F. [Ca2+]i was measured in parallel with the rate of insulin release. 50 nM 12-O-tetradecanoylphorbol-13-acetate (TPA), which may act via protein kinase C, stimulated insulin release and caused an increase in [Ca2+]i. Ca2+-free conditions eliminated the increase in [Ca2+]i and resulted in a reduced stimulation of insulin release by TPA. The Ca2+ channel blocker nitrendipine (300 nM) inhibited both the increase in [Ca2+]i and the increased rate of insulin secretion. Another phorbol ester, 4 beta-phorbol 12,13-didecanoate, which activates protein kinase C, also induced an increase in [Ca2+]i and in the rate of insulin release, while 4 alpha-phorbol 12,13-didecanoate, which fails to stimulate protein kinase C, was without effect. Further studies with bis-oxonol as an indicator of membrane potential showed that TPA depolarized the beta-cell plasma membrane. From these results, it is concluded that TPA depolarizes the plasma membrane, induces the opening of Ca2+ channels in the RINm5F beta-cell plasma membrane, increases [Ca2+]i, and results in insulin secretion. The action of TPA was next compared with that of a depolarizing concentration of KC1 (25 mM), which stimulates insulin secretion simply by opening Ca2+ channels. TPA consistently elicited less depolarization, a smaller rise of [Ca2+]i, but a greater release of insulin than KC1. Therefore an additional action of TPA is suggested, which potentiates the action of the elevated [Ca2+]i on insulin secretion.

Topics: Adenoma, Islet Cell; Animals; Benzofurans; Calcium; Carbachol; Cell Line; Cell Membrane; Cytosol; Ethers; Fluorescent Dyes; Fura-2; Insulinoma; Ionomycin; Kinetics; Membrane Potentials; Pancreatic Neoplasms; Potassium Chloride; Rats; Tetradecanoylphorbol Acetate